What Is an API Key?

Knock, knock. Who’s there? API client. API client who? This little digital chat happens billions of times a day in the world of IT. As more companies undertake digital transformation initiatives, they are exposing more of their applications and data sources through application programming interfaces (APIs). Indeed, virtually all modern software applications rely on these standards-based interfaces to connect with user devices and other applications. For the sake of security and reliability, it is essential to grant API access only to API clients that can verify their identities. The API key makes this happen, allowing the API client to assert its identity.

An API key is a unique bit of code that identifies the API client to the API. It’s like an ID card. It might look something like this: e7062c5b-d95d-4fa5-af31-52cb6e662816. Any number of platforms can generate the keys. When the API client invokes the API, the API “asks” for the API key. Once the client presents the key, the API grants access. Most API keys are static. They remain in effect until they are revoked.

API keys have two main purposes. One is authentication, a step that verifies that an API client is what it says it is. The API key signifies that the API client has permission to invoke the API. The process occurs at the API endpoint or API server.

The second purpose is authorization, which determines the API functions that the API client is entitled to access. After all, an API may represent more than one function. And it’s likely that not every API client will be authorized to use them all. One API client may get access to data set A, while another API client gets access to data sets A and B, and so forth. To realize this objective, the API project may assign more than one API key, with each key entitling the client to distinct access management rights.

API keys work in a fairly straightforward “Show us your ID” process, sort of like going through the TSA checkpoint at the airport. When the API client requests access at the API endpoint, the API checks its client database for the key. If the key being presented matches the key in the database, the API client is allowed to access whatever data and functionality is made available through the API.

The owners of the API can also use the API key to monitor API activity. For example, they can track the number and types of requests being made, because each request links back to a specific API key. This capability has a useful security benefit, as well. If a malicious actor has stolen an API key, for example, then that key’s activities can provide evidence of an attack — potentially enabling API security tools to shut down access before the attack does any serious damage.

The best uses for API keys occur in situations where the API owner wants to control API traffic. Requiring an API key obstructs traffic sources of unknown origin or questionable integrity. On a related note, API keys are useful when API owners want to monitor API traffic patterns. They might want to do this for security reasons, e.g., to detect malicious traffic or denial-of-service (DoS) attacks. Or they may want to measure traffic to better understand how to optimize API performance or negotiate terms with API users.

An API key is an identifier for the API client, but it differs from a set of API account credentials. The distinctions arise in several areas. For one thing, the API key identifies application requests but not users on an individual basis. Indeed, hundreds of end users could access an API through the same API client, and the API key, on its own, cannot distinguish between them.

To address this limitation of access control, some APIs require users to create accounts. Though API user accounts vary in structure, they tend to resemble software user accounts. They might mandate that the user set up a unique username and password. The API account credentials might also include an authorization token, such as one based on OAuth standards. With API account credentials, the API owner can know exactly which end user has accessed the API.

When implementing API keys within REST APIs, developers must follow best practices to ensure security and scalability. One approach is to assign different API keys for various applications, allowing for better control over API usage and access. Each API key can be assigned specific permissions based on the endpoints the application needs to access.

By managing multiple API keys, developers can isolate traffic, making it easier to track performance and detect potential abuse. REST APIs often involve frequent API calls, which makes using API keys for traffic segregation and management even more critical. Developers can also utilize an SDK to integrate REST APIs securely into their applications, ensuring proper authentication and authorization processes are followed.

API keys play an important role in managing and securing API calls, acting as an identifier for the application or client making the request. Once an API key is embedded in a call header, it authenticates the application’s access to the API endpoint. With this setup, API management tools can track and log all incoming API calls associated with that particular key. This level of monitoring allows developers to assess traffic patterns, identify anomalies in application traffic, and ensure that API resources are being accessed properly.

Monitoring the usage of API keys is critical, especially when managing large volumes of requests from various clients across platforms like iOS and Android. With the right API management solution, you can track metrics such as response times, failed requests, and overall usage to ensure your APIs are functioning optimally and securely.